1. Field of the Invention
The present invention relates generally to a data processing unit employing a microcomputer unit, which is mounted on an automotive vehicle. More specifically, the present invention relates to an improvement for the input unit of a data processing unit which is capable of eliminating noise contained in sensor signals or preventing a data processing system malfunction caused by input signal containing noise.
2. Description of the Related Art
As is known to those skilled in the art, in recent years, it has become quite popular to automatically control various vehicle systems by using a data processing unit including a microcomputer unit. The data processing unit is employed on the automotive vehicle for automatically controlling internal combustion engine systems such as the ignition system, exhaust gas recirculation system, fuel injection system and so on. The data processing system is further utilized for controlling various vehicle indicators, such as, for example, a navigation meter. Further, the data processing system is used for controlling various vehicle equipment, such as an automatic tuning device for a radio receiver of the vehicle mounted type. As stated above, the data processing system can be utilized for controlling various means or devices on the vehicle. An engine control system first detects various engine running variables such as air flow rate, engine speed, and temperature, and then controls the fuel injection amount, ignition timing, and exhaust-gas recirculation rate, and provides alarms indicative of abnormal states, based on these detected sensor signals. However, the detected signals are subject to noise interference. If such erroneous signals are applied to the engine control system, it becomes impossible to control the system under optimal conditions, and therefore the engine running performance, exhaust gas purification performance, and so on may deteriorate.
In addition to these problems, if the sensor signals are affected by noise, spurious alarms for catalyst temperature, for example, may be generated. This is at least an annoyance to the driver, but could possibly be a dangerous distraction.
Such abnormal signals may result not only from noise but also from noise-disturbed malfunctions of signal input devices such as A-D convertors or counters.
Causes of the signal disturbance include electrical noise (for example, ignition signals) interfering with the input line, while causes of A-D convertor malfunctions include electrical noise interfering with the power supply line.
The above A-D converter malfunction can readily be prevented by providing means to separate the power supply line into another system. However, it is very difficult and costly to completely eliminate electric noise from the input line by only providing conventional shield wires or filters, since the sensors detecting various engine running variables are usually positioned in the engine compartment and are thus positioned in the vicinity of noise sources such as ignition devices.
The present invention provides an improved data processing system which is capable of eliminating harmful effects caused by noise contained in the input signals fed from various sensors.